Laser drive device, optical head, and optical information processor

ABSTRACT

To provide a laser driving apparatus which is inexpensive and has high reliability in spite of using a plurality of light sources, since a multi-wavelength light source is required for treating different kinds of optical disks such as CD, DVD or the like. In a two-wavelength LD apparatus including: a semiconductor laser  1   a ; a semiconductor laser  1   b ; and a photo detector  2 , optical outputs of the semiconductor lasers  1   a   , 1   b  are controlled by APC circuits  6   a   , 6   b  on the basis of respective voltage values of variable resistors  4   a   , 4   b  connected in series to the photo detector  2 . Alternatively, in the two-wavelength LD apparatus including: the semiconductor laser  1   a ; the semiconductor laser  1   b ; and the photo detector  2 , the optical outputs of the semiconductor  1   a   , 1   b  are controlled by the APC circuits  6   a   , 6   b  on the basis of respective intermediate potentials of variable resistors  4   a   , 4   b  connected in parallel with the photo detector  2.

This application is a U.S. National Phase Application of PCTInternational Application PCT/JP01/00848.

1. Technical Field

The present invention relates to an optical information processingapparatus for recording, reproducing or erasing information on anoptical medium or magneto-optical medium such as an optical disk or anoptical card, and more particularly an optical head apparatus whichemits laser beams having different wavelengths and a laser drivingapparatus used in the optical head apparatus.

2. Background Art

An optical memory technology which uses an optical disk having apit-shaped pattern as a memory medium having a high density and a largecapacity is finding extending application in a digital audio-disk, avideo disk, a document file disk and a data file and the like.

By the optical memory technology, information is recorded and reproducedon an optical disk with high accuracy and high reliability by way of afinely condensed light beam. Recording and reproducing operations dependonly on an optical system used for the optical memory technology.

Basic functions of an optical head apparatus which is a principal partof the optical system are classified roughly into converging for forminga diffraction limited fine spot, focal point control and trackingcontrol for the above described optical system, and pit signaldetection. These functions are realized by combination of various kindsof optical systems and photoelectric conversion detecting systemsdepending on purposes and applications.

On the other hand, an optical disk having a high density and a largecapacity which is referred to as DVD has recently been put to practicaluse and spotlighted as an information medium which permits processing alarge amount of information such as animations. The DVD optical diskadopts a smaller pit size on an information recording surface so as tohave a recording density higher than that on a compact disk (hereinafterabbreviated as a CD) which is a conventional optical disk. Accordingly,an optical head apparatus which records and reproduces (information on)the DVD optical disk uses a light source and a converging lens having awavelength and a numerical aperture (hereinafter abbreviated as NA) fordetermining a spot diameter which are different from those for the CD.For reference, a wavelength of a light source is approximately 0.78 μmand an NA of a converging lens is 0.45 for the CD, whereas a wavelengthof a light source is approximately 0.63 to 0.68 μm and an NA isapproximately 0.6 for the DVD optical disk.

For recording and reproducing (information on) two kinds of opticaldisks of the CD and the DVD optical disk by one optical informationprocessing apparatus, an optical head apparatus having two opticalsystems is required. Since a CD-R which has recently been usedfrequently as a derivative form of the CD permitting additional writinguses a reflecting film on a disk which is optimalized to a wavelength of0.78 μm and does not allow information reproduction at the wavelengthfor the DVD in particular, an optical information processing apparatuswhich records and reproduces information not only on DVD and CD but alsoon the CD-R must have two light sources having wavelengths of 0.78 μmand 0.63 to 0.68 μm.

From demands for compact and thin configuration and a lower cost of theoptical head apparatus, on the other hand, an optical system tends to beused commonly for the CD and DVD, and there are adopted, for example, asystem which switches only converging lenses between two kinds for theCD and DVD optical disk and a system which uses also a converging lenscommonly while mechanically or optically enlarging only an NA for theDVD optical disk and reducing the NA for the CD.

Furthermore, there has recently been developed a technology whichintegrates also a light source by forming an infrared laser emittinglayer and a red laser emitting layer in a chip of semiconductor laser(for example, LD: laser diode). Furthermore, there has been developed atwo-wavelength light source which has two kinds of semiconductor laserchips mounted in a single package.

The above described two light sources will hereinafter be referred tocollectively as two-wavelength LDs for convenience. Description will nowbe made of a driving method for the two-wavelength LD.

FIG. 10 is a block diagram of a conventional LD driving circuit, inwhich reference numeral 1 denotes a semiconductor laser, referencenumeral 2 denotes a photodiode which is a photodetector for monitoringan output from the semi conductor laser. Reference numeral 3 denotes acommon terminal, reference numeral 4 denotes a variable resistor,reference numeral 5 denotes an operational amplifier and referencenumeral 6 denotes an automatic power control circuit (hereinafterabbreviated as APC circuit).

Description will now be made of operations of the LD driving circuitwhich is configured as described above. In FIG. 10, the common terminal3 is maintained at a positive potential with a power source apparatus(not shown). When the APC circuit 6 starts operating, a current issupplied to the semiconductor laser 1 to emit rays from thesemiconductor laser 1. When the photodiode 2 receives a portion of therays emitted from the semiconductor laser 1, a current corresponding toan intensity of the emitted rays is supplied from the common terminal 3to ground by way of the photodiode 2 and the variable resistor 4,thereby generating a voltage across both ends of the variable resistor4. The voltage of the variable resistor 4 is detected by the operationalamplifier 5 and fed back to the APC circuit 6. The APC circuit 6controls the current supplied to the semiconductor laser 1 so that thevoltage of the variable resistor 4 is a predetermined voltage, therebymaintaining an optical output from the semiconductor laser 1 constant. Aresistance value of the variable resistor 4 is adjusted so that theoptical output from the semiconductor laser 1 has a desired value.

Though the above described conventional example uses an outputmonitoring photodetector for a semiconductor laser, a two-wavelength LDwhich has recently been under development uses only an output monitoringphotodetector for two light sources in most cases as shown in FIG. 11.

FIG. 11 is a circuit block diagram of the two-wavelength LD, in whichreference numeral 1 a denotes a first semiconductor laser and referencenumeral 1 b denotes a second semiconductor laser. Reference numeral 2denotes a photodiode which is a photodetector for monitoring outputsfrom the semiconductor lasers. Reference numeral 3 denotes a commonterminal. Due to demands for a low cost and a compact configuration ofthe light source, the circuit uses only one photodetector 2 and only oneoutput terminal of the photodetector 2. Though 1 a and 1 b are twosemiconductor lasers in FIG. 11, these lasers may be separate lightemitting layers of a single laser chip.

When the above described LD driving circuit is used as a circuit fordriving such a two-wavelength LD as that shown in FIG. 11, the circuithas such a configuration as that shown in FIG. 12.

FIG. 12 is a block diagram of a circuit for driving the two-wavelengthLD, in which members identical to those in FIG. 11 are denoted byidentical reference numerals with no description in particular. In FIG.12, reference numerals 4 a and 4 b denote variable resistors, referencenumerals 5 a and 5 b denote operational amplifiers, reference numerals 6a and 6 b denote APC circuits, and reference numerals 7 a and 7 b denoteelectronic switches.

Semiconductor laser driving operations in FIG. 12 will be describedbriefly. For driving first semiconductor laser 1 a, the electronicswitch 7 a is set in a connected condition, whereas the electronicswitch 7 b is set in a disconnected condition.

When the first semiconductor laser 1 a is allowed by the APC circuit 6 ato start emitting rays, a current is supplied to a photodetector 2 byway of the variable resistor 4 a by functions of the electronic switches7 a and 7 b. Subsequently, the first semiconductor laser 1 a can bedriven at a desired optical output by adjusting a resistance value ofthe variable resistor 4 a as in the conventional LD driving circuit.

For driving the second semiconductor laser 1 b, the electronic switch 7a is set in a disconnected condition, whereas the electronic switch 7 bis set in a connected condition. Since a current is supplied to thephotodetector 2 by way of the variable resistor 4 b, the secondsemiconductor laser can be glowed at a desired optical output byadjusting a resistance value of the variable resistor 4 b. For the abovedescribed operations, the APC circuits 6 a and 6 b as well as theelectronic switches 7 a and 7 b are switched automatically andselectively by a control system (not shown).

However, the above described two-wavelength LD driving circuit has aconfiguration which requires the electronic switches 7 a and 7 b,thereby posing a problem to enhance a cost.

Furthermore, the above described two-wavelength LD driving circuits alsohas a problem that the circuit allows voltage values detected with theoperational amplifiers 5 a and 5 b to be changed due to changes ofresistance values which are caused by temperature changes in theconnected conditions of the electronic switches 7 a and 7 b, therebychanging the outputs from the semiconductor lasers 1 a and 1 b.Accordingly, the two-wavelength LD driving circuit poses a problem toenhances costs and deteriorates temperature characteristics of anoptical head apparatus and an optical information processing apparatuswhich use a two-wavelength LD driven by the two-wavelength LD drivingcircuit.

DISCLOSURE OF THE INVENTION

The present invention has been achieved to solve the problems describedabove and has an object to provide a laser driving apparatus which isinexpensive and free from deterioration of characteristics as well as anoptical head apparatus and an optical information processing apparatuswhich use the laser driving apparatus.

One aspect of the present invention is a laser driving apparatuscomprising:

n laser light sources L1 to Ln (n is a natural number equal to or largerthan 2);

a photodetector of detecting rays emitted from said n laser lightsources;

n variable resistors VR1 to VRn connected to said photodetector;

voltage detecting means of detecting n kinds of voltages V1 to Vnrelated to said variable resistors; and

control means of controlling outputs of said laser light sources so thatdetected corresponding voltage values are predetermined values, and

said variable resistors VR1 to VRn are connected in series to oneanother,

the object of the voltage detection is one variable resistor or a serialcircuit composed of a plurality of variable resistors connected inseries, and

the variable resistors or serial circuits always include variableresistors which are different from each other.

Another aspect of the present invention is A laser, driving apparatuscomprising:

n laser light sources L1 to Ln (n is a natural number equal to or largerthan 2);

a photodetector of detecting rays emitted from said n laser lightsources;

n variable resistors VR1 to VRn connected to said photodetector;

voltage detecting means of detecting n kinds of voltages V1 to Vnrelated to said variable resistors; and

control means of controlling outputs of said laser light sources so thatdetected corresponding voltage values are predetermined values, and

said variable resistors VR1 to VRn are connected in parallel with oneanother and

said voltage detecting means detects voltages V1 to Vn of middlepotentials of said variable resistors relative to a reference voltage.

Still another aspect of the present invention is a laser drivingapparatus comprising:

n laser light sources L1 to Ln (n is a natural number equal to or largerthan 2);

a photodetector of detecting rays emitted from said n laser lightsources;

n variable resistors VR1 to VRn connected to said photodetector;

voltage detecting means of detecting n kinds of voltages V1 to Vnrelated to said variable resistors; and

control means of controlling an output of said laser light source sothat a detected corresponding voltage value is a predetermined value,and

said variable resistors VR1 to VRn are connected partially in series toone another and connected partially in parallel with one another,

with regard to a group of variable resistors connected in series,

the object of the voltage detection is one variable resistor or a serialcircuit composed of a plurality of variable resistors connected inseries,

the variable resistors or the serial circuits always include variableresistors different from each other, and

with regard to a group of variable resistors connected in parallel, saidvoltage detecting means detects voltages of middle potentials of thevariable resistors connected in parallel relative to a referencevoltage.

Yet still an other aspect of the present invention is the laser drivingapparatus wherein

said n is two and said variable resistors are connected in series, and

said voltage detecting means detects a voltage across both ends of eachof said variable resistors.

Still yet another aspect of the present invention is the laser drivingapparatus,

said n is two and said variable resistors are connected in series, and

said voltage detecting means detects a voltage across both ends of oneof said variable resistors, detects a voltage across both ends of aserial circuit composed of said both variable resistors and detectsvoltages across both ends of the variable resistors respectivelyutilizing detected voltage of these two detected.

A further aspect of the present invention is the laser drivingapparatus,

said n is two and said variable resistors are connected in series, and

said voltage detecting means (1) detects a voltage across both ends ofone of said variable resistors which is connected to a referencepotential, (2) detects a potential of a terminal of the other variableresistor which is not connected to said one variable resistor relativeto said reference potential, and (3) detects a voltage across both endsof said other variable resistor by subtracting said detected voltageacross both the ends from said detected potential.

A still further aspect of the present invention is the laser driving:apparatus,

said variable resistors are connected in series and one of the variableresistors is connected to a predetermined reference potential, and

said voltage detecting means detects a potential of a side of said oneof the variable resistors which is not connected to the referencepotential relative to the reference potential and a potential of theother variable resistor which is not connected to said one of thevariable resistors relative to said reference potential.

A yet further aspect of the present invention is an optical headapparatus, comprising:

the laser driving apparatus;

means of condensing rays emitted from said laser driving apparatus ontoan optical information medium; and

a photodetector of detecting reflected rays from said opticalinformation medium.

A still yet further aspect of the present invention is an opticalinformation processing apparatus, comprising at least:

a driving mechanism for an optical information medium;

The optical head apparatus;

a focus servo mechanism using a focus error signal and a tracking errorsignal respectively obtained from said optical head apparatus;

a tacking servo mechanism;

an electric circuit for realizing said servo mechanism; and

a power source.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit block diagram of an LD driving apparatus accordingto a first embodiment of the present invention;

FIG. 2 is a circuit block diagram of an LD driving apparatus accordingto a second embodiment of the present invention;

FIG. 3 is a circuit block diagram of an LD driving apparatus accordingto a third embodiment of the present invention;

FIG. 4 is a circuit block diagram of an LD driving apparatus accordingto a fourth embodiment of the present invention;

FIG. 5 is a circuit block diagram of an LD driving apparatus accordingto a fifth embodiment of the present invention;

FIG. 6 is a circuit diagram showing various kinds of connection modesfor variable resistors according to an embodiment of the presentinvention;

FIG. 7 is a circuit block diagram of an LD driving apparatus accordingto a sixth embodiment of the present invention;

FIG. 8 is configurational diagram of an optical head apparatus accordingto a seventh embodiment of the present invention;

FIG. 9 is a configurational diagram of an optical information processingapparatus according to an eighth embodiment of the present invention;

FIG. 10 is a block diagram of a conventional LD driving circuit;

FIG. 11 is a circuit block diagram of a two-wavelength LD; and

FIG. 12 is a block diagram of a driving circuit for a two-wavelength LD.

DESCRIPTION OF SYMBOLS

1 a First semiconductor laser

1 b Second semiconductor laser

2 Photodiode

3 Common terminal

4 a, 45 b Variable resistor

5 a, 5 b Operational amplifier

6 a, 6 b APC circuit

BEST MODE FOR CARRYING OUT THE INVENTION

Now, description will be made of preferred embodiments of the presentinvention with reference to the accompanying drawings.

First Embodiment

FIG. 1 is a circuit block diagram of an LD-driving apparatus accordingto a first embodiment of the present invention. In FIG. 1, members whichare identical to those shown in FIG. 12 are denoted by identicalreference numerals with no description in particular. Different fromFIG. 12, FIG. 1 shows variable resistors 4 a and 4 b which are which areconnected in series to a photodetector 2, and an operational amplifier 5b which is connected to both ends of the variable resistor 4 b. Theoperational amplifier is an example of voltage detecting means accordingto the present invention. An operational amplifier is used as voltagedetecting means also in embodiments which are described later.

Description will be made of operations of the two-wavelength LD drivingapparatus according to the first embodiment of the present inventionwhich is configured as described above.

When a first semiconductor laser 1 a is glowed by an APC circuit 6 awhich is an example of control means according to the present invention,a current is supplied to the photodetector 2 by way of the variableresistors 4 b and 4 a. At this time, generated across both ends of eachof the variable resistors 4 b and 4 a are voltages which correspond toresistance values of the variable resistors. The voltage across both theends of the variable resistor 4 a is detected by an operationalamplifier 5 a and fed back to the APC circuit 6 a.

The APC circuit 6 a controls a driving current for the firstsemiconductor laser 1 a so that the voltage of the variable resistor 4 ais a predetermined voltage. By adjusting a resistance value of thevariable resistor 4 a in advance, it is possible to glow the firstsemiconductor laser 1 a at a desired optical output.

For driving a second semiconductor laser 1 b, a current is supplied tothe photodetector 2 by way of the variable resistors 4 b and 4 a in amanner like that described above when an APC circuit 6 b which is anexample of the control means according to the present invention startssupplying a current to the second semiconductor laser 1 b. At this time,generated across both ends of each of the variable resistors 4 b and 4 aare voltages corresponding to a resistance values of the variableresistors.

The voltage across both the ends of the variable resistor 4 b isdetected by the operational amplifier 5 b and fed back to the APCcircuit 6 b. The APC circuit 6 b controls a driving current for thesecond semiconductor laser 1 b so that the voltage of the variableresistor 4 b is a predetermined voltage. By adjusting a resistance valueof the variable resistor 4 b in advance, it is possible to glow thesecond semiconductor laser 1 b at a desired optical output.

The LD driving apparatus according to this embodiment is configured toconnect variable resistors in series in a number corresponding to anumber of semiconductor lasers so that each operational amplifierdetects a voltage across both ends of each variable resistor asdescribed above, thereby making it possible to realize inexpensive andstable operations of members except electronic switches.

Though the embodiment is configured to use the two semiconductor lasers,it is needless to say that an optical output of each semiconductor lasercan be controlled constant even when three or more (the number of n)semiconductor lasers are used by connecting variable resistors in seriesin a number corresponding to a number of the semiconductor lasers,detecting a voltage value of each variable resistor and feeding back thevoltage value.

Second Embodiment

FIG. 2 is a circuit block diagram of an LD driving apparatus accordingto a second embodiment. In FIG. 2, members which are identical to thoseshown in FIG. 1 are denoted by identical reference numerals with nodescription in particular. Reference numeral 5 c denotes an operationalamplifier.

In a configuration shown in the drawing, items which are different fromthose in FIG. 1 are an input of an operational amplifier 5 b which isgrounded and the operational amplifier 5 c which takes a differencebetween an output from the operational amplifier 5 b and that from anoperational amplifier 5 a, and feeds back the difference to an APCcircuit 6 b. In the second embodiment, these operational amplifierscompose voltage detecting means according to the present invention.

The two-wavelength LD driving apparatus according to the secondembodiment which is configured as described above remains substantiallyunchanged from the two-wavelength driving apparatus according to thefirst embodiment in operations for driving semiconductor lasers 1 a and1 b, and provides a similar effect, but is differently configured to usethe operational amplifiers 5 b and 5 c as means of detecting a voltageacross both ends of a variable resistor 4 b.

In this configuration, the input section which is grounded out of inputsof the operational amplifiers 5 a and 5 b is common in an actualcircuit, and input terminals other than that which is grounded of theoperational amplifiers 5 a and 5 b at a first stage as seen from a sideof the APC circuit compose two channels in total, whereby the secondembodiment makes it possible to reduce a number of terminals of theoperational amplifiers as compared with the first embodiment which usesthree channels and provides an effect to permit simplifying aconfiguration of a circuit as a whole.

Third Embodiment

FIG. 3 is a circuit block diagram of an LD driving apparatus accordingto a third embodiment. In FIG. 3, members which are identical to thoseshown in FIG. 2 denoted by identical reference numerals with nodescription in particular. Reference numeral 5 c denotes an operationalamplifier. In a configuration shown in the drawing, an operationalamplifier 5 b is omitted as an item which is different from theconfiguration shown in FIG. 2.

In the two-wavelength LD driving apparatus according to the thirdembodiment which is configured as described above, operations fordriving semiconductor lasers 1 a and 1 b remain substantially unchangedfrom those in the first embodiment and a similar effect is obtained, butthe third embodiment is configured differently in that the operationalamplifiers 5 a and 5 c are used as means of detecting a voltage acrossboth ends of a variable resistor 4 b.

Since one of inputs of the operational amplifier 5 c is an output of theoperational amplifier 5 a in this configuration, the third embodimentpermits integrating the operational amplifiers 5 a and 5 c with eachother in actual manufacturing, thereby composing a circuit ofoperational amplifiers in a number smaller than that of the operationalamplifiers used in the second embodiment and provides an effect tofurther simplify a configuration of a circuit as a whole by reducingexternal terminals.

Fourth Embodiment

FIG. 4 is a circuit block diagram of an LD driving apparatus accordingto a fourth embodiment. In FIG. 4, members which are identical to thosein FIG. 2 are denoted by identical reference numerals with nodescription in particular. Points of a configuration shown in thedrawing which are different from that shown in FIG. 2 are that anoperational amplifier 5 c is omitted and that an output from anoperational amplifier 5 b is input directly into an APC circuit 6 b.

In the two-wavelength LD driving apparatus according to this embodimentwhich is configured as described above, operations for drivingsemiconductor lasers 1 a and 1 b remain substantially unchanged fromthose in the first embodiment and a similar effect is obtained, but thefourth embodiment is differently configured to use as a voltage to befed back to the APC circuit 6 b a potential difference between areference potential (a ground potential in the fourth embodiment) and apotential of a variable resistor 4 b on a side of a photodetector.

Accordingly, the fourth embodiment is different also in steps ofadjusting an optical output from a laser. Specifically, a resistancevalue of a variable resistor 4 a is adjusted by glowing a firstsemiconductor laser 1 a corresponding to a variable resistor 4 a set ata potential close to the reference potential and then a resistance valueof the variable resistor 4 b is adjusted by glowing a secondsemiconductor laser 1 b corresponding to the variable resistor 4 b.

This is because a potential difference between the reference potentialand the potential on a side of the variable resistor 4 b is changed whenthe variable resistor 4 b is adjusted first and then the variableresistor 4 a is adjusted.

In addition, a predetermined voltage to be utilized for control in theAPC circuit 6 b needlessly has a value which is determined taking totalresistance of the variable resistors 4 a and 4 b into consideration.

This configuration provides effects to permit composing a circuit with asmall number of operational amplifiers like the third embodiment,simplify a circuit composition by reducing external terminals, and allowa power consumption to be lower than that of the third embodiment bypreventing operational amplifiers other than that for a glowingsemiconductor laser from being operated since the operational amplifiers5 a and 5 b operate independently of each other.

Be Though the above described first to fourth embodiments are examplesin each of which two variable resistors are connected in series, it isneedless to say that three or more variable resistors may be connectedin series. FIG. 6(a) shows an example in which three variable resistorsare connected in series. In this case, voltage which are detected to beutilized for control may be voltages across end of variable resistors 40a, 40 b and 40 c respectively or other voltages which are describedbelow. That is, when the variable resistors 40 a, 40 b and 40 c aredenoted consecutively as first, second and third variable resistors, afirst voltage out of three kinds, of voltages is taken as a voltageacross both ends of the variable resistor 40 a, a second voltage istaken as a voltage across both ends of a serial circuit composed of thevariable resistors 40 a and 40 b, and, a third voltage is taken as avoltage across both ends of the variable resistor 40 c.

Alternately, it is possible to take the first voltage out of the threekinds of voltage as the voltage across both the ends of the variableresistor 40 a, take the second voltage as the voltage across both theends of the serial circuit of the variable resistors 40 a and 40 b, andtake the third voltage as a voltage across both ends of a serial circuitcomposed of the variable resistors 40 a, 40 b and 40 c.

Alternately, it is possible to take the first voltage out of the threekinds of voltages as the voltage across both the ends of the variableresistor 40 a, take the second voltage as the voltage across both theends of the serial circuit of the variable resistors 40 a and 40 b, andtake the third voltage as a voltage as a voltage across both ends of aserial circuit composed of the variable resistors 40 b and 40 c.

Thus, for detecting a voltage which is to be utilized to control a laserlight source, the object of the detection is not limited to one variableresistor but may be a serial circuit composed of a plurality of variableresistors.

When a serial circuit including a variable resistor which has alreadybeen adjusted is to be used as an object as described above, however,the serial circuit must include a variable resistor which has not beenadjusted yet since the variable resistor which has already been adjustedcannot be changed. The variable resistor which has not been adjusted yetmust be adjusted for adjusting an optical output of a laser.

That is, when a plural kinds of voltages are necessary, a serial circuitwhich is to be an object of detection of k′th (k=1 to n) voltage Vk andcomposed of a plurality of variable resistors must include at least k′thresistor which has not been adjusted yet in addition to first to k−1′thresistors which have already been adjusted. Ordinal numbers of the k′thand n′th resistors are counted successively from an end of a group ofvariable resistors which are connected in series.

In short, the variable resistors or the serial circuits must alwaysinclude variable resistors which are different from each other.

Fifth Embodiment

FIG. 5 is a circuit block diagram of an LD driving apparatus accordingto a fifth embodiment. In FIG. 5, members which are identical to thoseshown in FIG. 4 are denoted by identical reference numerals with nodescription in particular. In FIG. 5, reference numerals 100 a and 100 bdenote sliders of variable resistors 4 a and 4 b respectively, andpotential differences between potentials of the sliders 100 a, 100 b(hereinafter referred to as middle potentials of the variable resistors4 a, 4 b) and a ground potential can be changed by sliding the sliders100 a, 100 b along resistor lines.

A configuration shown in the drawing is different from a configurationshown in FIG. 4 in a point that the variable resistors 4 a and 4 b areconnected to a photodetector 2 so that the variable resistors are inparallel with each other, and a point that the middle potentials of thevariable resistors 4 a and 4 b are input into operational amplifiers 5 aand 5 b.

Description will be made of operations of the LD driving apparatusaccording to the fifth embodiment of the present invention which isconfigured as described above.

When a first semiconductor laser 1 a is glowed by an APC circuit 6 a, acurrent is supplied to the photodetector 2 by way of the variableresistors 4 a and 4 b. At this time, a voltage is generated across bothends of the variable resistors 4 a and 4 b in accordance with a totalresistance value of the variable resistors. The middle potential of thevariable resistor 4 a is detected by the operational amplifier 5 a andfed back to an APC circuit 6 a.

The APC circuit 6 a controls a driving current for the firstsemiconductor laser 1 a so that the middle potential of the variableresistor 4 a is a predetermined potential. The first semiconductor laser1 a can be glowed at a desired optical output by adjusting the slider100 a of the variable resistor 4 a.

When a second semiconductor laser 1 b is to be driven next, an APCcircuit 6 b starts supplying a current to the second semiconductor laser1 b, whereby a current is supplied to the photodetector 2 by way of thevariable resistors 4 a, 4 b in a manner similar to that described above.

The middle potential of the variable resistor 4 b is detected by theoperational amplifier 5 b and fed back to the APC circuit 6 b. The APCcircuit 6 b controls a driving current for the second semiconductorlaser 1 b so that the middle potential of the variable resistor 4 b is apredetermined potential. The second semiconductor laser 1 b can beglowed at a desired optical output by adjusting the slider 100 b of thevariable resistor 4 b.

The LD driving apparatus according to the fifth embodiment is configuredto connect variable resistors in parallel with one another in a numbercorresponding to a number of semiconductor lasers so that individualoperational amplifiers detect middle potentials of the variableresistors respectively as described above, thereby making it possible toobtain an effect similar to that of the fourth embodiment.

Though the input to the operational amplifier 5 b is higher than that tothe operational amplifier 5 a and the voltages fed back to the APCcircuits 6 a and 6 b are in an unequal relation in the fourthembodiment, the fifth embodiment does not require taking such an unequalrelation into consideration and provides an effect to permit using theAPC circuits 6 a and 6 b which are of an identical kind.

Furthermore, it is needless to say that three or more variable resistorsmay be connected in parallel with one another.

In addition, variable resistors of the LD driving apparatus according tothe present invention may consist of a serial circuit portion (40 a, 40b and 40 c) and a parallel circuit portion (40 d, 40 e and 40 f) whichis connected in parallel, for example, with the variable resistor 40 bas shown in FIG. 6(b). Though the parallel circuit portion includes 40 bstrictly speaking, 40 b is included herein in the serial circuitportion.

In such a case, description made with reference to the first to fourthembodiment applies to the above described serial circuit portion anddescription made with reference to the fifth embodiment applies to theabove described parallel circuit portion.

Sixth Embodiment

FIG. 7 shows an LD driving apparatus according to a sixth embodiment. InFIG. 7, members which are identical to those shown in FIG. 5 are denotedby identical reference numerals with no description in particular.

A configuration shown in the drawing is different from that shown inFIG. 5 in a point that semiconductor lasers 1 a and 1 b are accommodatedin a cabinet 101, and in another point that a photodetector 2 isdisposed outside the above described cabinet 101 as a separate part.

This is a configuration in case of an apparatus such as a CD-R, CD-RWrecording apparatus or a DVD-RAM, DVD-R, DVD-RW recording apparatuswhich uses the photodetector 2 as a front optical monitor when it isnecessary to strictly manage light amounts on disk surfaces.

Though the LD driving apparatus according to the sixth embodiment whichis configured as described above remains substantially unchanged inoperations to drive the semiconductor lasers 1 a and 1 b from the LDdriving apparatus according to the fifth embodiment, the LD drivingapparatus according to the sixth embodiment provides not only an effectto maintain an optical output constant by controlling the current fordriving the semiconductor lasers 1 a and 1 b according to a light amountdetected with the photodetector 2 but also an effect to control theoptical output by dynamically controlling the APC circuits.

This configuration makes it possible to control light amounts on disksurfaces of lasers respectively with a photodetector, thereby providingan effect to permit reducing a number of parts.

Though variable resistors 4 a and 4 b are connected in parallel witheach other in the sixth embodiment, this method is not limitative andany one of connection modes described with reference to the abovedescribed first to fifth embodiments may needlessly be adopted.

FIGS. 8(a) and 8(b) are diagrams showing a configuration of an opticalhead apparatus according to a seventh embodiment. In these drawings,reference numeral 8 denotes a two-wavelength light receiving-emittingunit which has a two-wavelength LD, an photodetector for detectingreflected light from an optical information medium and a hologram.Reference numeral 9 denotes the hologram which has a function to leadrays to the above described photodetector by refracting the rays.Reference numeral 10 denotes a condenser lens, reference numeral 11denotes a bending mirror and reference numeral 12 denotes a wavelengthselective aperture which transmits all rays having a wavelength of 0.65μm and rays having a wavelength of 0.78 μm only within a range of 0.45in terms of an NA of an objective lens 13. Reference numeral 13 denotesthe objective lens, reference numeral 14 denotes a CD optical disk andreference numeral 115 denotes a DVD optical disk.

Furthermore, FIG. 8(a) shows a reproducing condition of a CD where alaser beam which is emitted from the two-wavelength lightreceiving-emitting unit 8 and has a wavelength of 0.78 μm is transformedby the condenser lens 10 into a parallel beam, led along an optical pathbent by the bending mirror 11 and incident on the wavelength selectiveaperture 12.

The laser beam which is stopped down by the wavelength selectiveaperture 12 is condensed by the objective lens 13 onto the CD opticaldisk 14. The laser beam which is reflected by the CD optical disk 14 isreturned reversely from the objective lens 13 by way of the bendingmirror 11 to the condenser lens 10, diffracted by the hologram 9, andphotoelectrically converted and detected as an electric signal by thephotodetector of the two-wavelength light receiving-emitting unit 8.

Then, FIG. 8(b) shows a reproducing condition of a DVD where a laserbeam which is emitted from the two-wavelength light receiving-emittingunit 8 and has a wavelength of 0.65 μm is transformed by the condenserlens 10 into a parallel beam, led along the optical path bent by thebending mirror 11 and incident on the wavelength selective aperture 12.

The laser beam which has transmitted through the wavelength selectiveaperture 12 is condensed by the objective lens 13 onto the DVD opticaldisk 15. The laser beam which is reflected by the DVD optical-disk 15 isreturned reversely from the objective lens 13 by way of the bendingmirror 11 to the condenser lens 10, diffracted by the hologram 9, andphotoelectrically converted and detected as an electric signal by thephotodetector of the two-wavelength light receiving-emitting unit 8.

In either case of the CD optical disk and the DVD optical disk, theelectric signal which is photoelectrically converted and detected by thephotodetector is used as an rf signal in a pit row or a servo signal fortracing a pit row on the optical disk.

Furthermore, a known three-beam method is usable for tracking servo atthe CD reproducing time though not shown.

The optical head apparatus according to the seventh embodiment iscapable of obtaining a favorable temperature characteristic at a lowcost when the optical head apparatus uses the laser driving apparatusaccording to the embodiment of the present invention.

Eighth Embodiment

An optical information processing apparatus according to an eighthembodiment of the present invention will be described using FIG. 9. InFIG. 9, reference numeral 16 denotes the optical head apparatusdescribed with reference to the sixth embodiment, reference numeral 17denotes an optical disk and reference numeral 18 denotes a motor whichsupports and rotates the optical disk 17. Reference numeral 19 denotes acircuit board and reference numeral 20 denotes a power source.

The optical information processing apparatus according to the eighthembodiment which has a configuration described above operates asdescribed below. The optical disk 17 is rotated by the motor 18. Theoptical head apparatus 16 sends to the circuit board 19 a signal whichcorresponds to a positional relation to the optical disk 17. The circuitboard 19 calculates this signal and outputs a signal for slightly movingthe optical head apparatus 16 or an objective lens in the optical headapparatus 16. The optical head apparatus 16 or the objective lens in theoptical head apparatus 16 performs focus servo and tracking servo forthe optical disk 17 with a driving mechanism (not shown), therebyreading, writing or erasing information from or to the optical disk 17.Reference numeral 20 denotes the power source or a connector for anexternal power source from which electricity is supplied, to the circuitboard 19, the driving mechanism for the optical head apparatus, themotor 18 and the driving mechanism for the objective lens.

In addition, no problem is posed by disposing connecting terminals forthe power source or the external power source in each driving circuit.

The laser driving apparatus according to the present inventioncorresponds to the LD driving apparatus in each embodiment, thepotential detecting means according to the present invention correspondsto the operational amplifier in each embodiment and the output controlmeans according to the present invention corresponds to the APC circuitin each embodiment.

Though the semiconductor lasers are exemplified in an anode common modein the embodiments of the present invention, the semiconductor lasersmay needlessly be used in a cathode common mode when only a power sourceis replaced with a ground potential.

INDUSTRIAL APPLICABILITY

The present invention makes it possible to perform automatic powercontrol drive of a plurality of semiconductor lasers with aphotodetector and a plurality of variable resistors corresponding to thesemiconductor lasers as described above, thereby enabling to obtain alaser driving apparatus which is advantageous from viewpoints of a costand a temperature characteristic.

Furthermore, the present invention makes it possible to obtain anoptical head apparatus which is inexpensive and has a favorabletemperature characteristic.

Furthermore, the present invention makes it possible to obtain anoptical information processing apparatus which can cope with variousoptical disk media, and is inexpensive and favorable in a temperaturecharacteristic.

What is claimed is:
 1. A laser driving apparatus comprising: n laserlight sources L1 to Ln in which n is a natural number equal to or largerthan 2; a photodetector detecting rays emitted from said n laser lightsources; n variable resistors VR1 to VRn connected to saidphotodetector; a voltage detector detecting n different values ofvoltages V1 to Vn related to said n variable resistors; a controllercontrolling outputs of said laser light sources so that the detectedvoltage values are maintained at predetermined values, and said nvariable resistors VR1 to VRn are connected in series to one another,wherein each of the n different values of voltages V1 to Vn detected isa voltage across both ends of one variable resistor within said nvariable resistors, or a voltage across both ends of a serial circuitincluding at least two resistors within said n variable resistors.
 2. Alaser driving apparatus comprising: n laser light sources L1 to Ln inwhich n is a natural number equal to or larger than 2; a photodetectordetecting rays emitted from said n laser light sources; n variableresistors VR1 to VRn connected to said photodetector; a voltage detectordetecting n kinds of voltages V1 to Vn related to said n variableresistors; a controller controlling outputs of said laser light sourcesso that the detected voltage values are maintained at predeterminedvalues; said n variable resistors VR1 to VRn are connected in parallelwith one another and said voltage detecting means detects voltages V1 toVn of middle potentials of said n variable resistors relative to areference voltage.
 3. A laser driving apparatus comprising: n laserlight sources L1 to Ln in which n is a natural number equal to or largerthan 2; a photodetector detecting rays emitted from said n laser lightsources; n variable resistors VR1 to VRn connected to saidphotodetector; a voltage detector detecting n kinds of voltages V1 to Vnrelated to said n variable resistors; a controller controlling an outputof said laser light sources so that a detected corresponding voltagevalue has a predetermined value, and a group of variable resistorswithin said n variable resistors are connected in series to one anotherand another group of variable resistors within said n variable resistorsare connected in parallel with one another, wherein for the group ofvariable resistors connected in series, each of different values ofvoltages detected is a voltage across both ends of one variable resistorwithin said group of variable resistors connected in series, or avoltage across both ends of a serial circuit including at least tworesistors within said n variable resistors, and wherein for the othergroup of variable resistors connected in parallel, said voltagedetecting means detects voltages of middle potentials of the variableresistors connected in parallel relative to a reference voltage.
 4. Thelaser driving apparatus according to claim 1, wherein said n is two andsaid n variable resistors are connected in series, and said voltagedetecting means detects voltages across both ends of each of said nvariable resistors.
 5. The laser driving apparatus according to claim 1,wherein said n is two and said n variable resistors are connected inseries, and said voltage detecting means detects a voltage across bothends of one of said n variable resistors, and detects a voltage acrossboth ends of a serial circuit including said both variable resistors andby utilizing these two detected voltages detects a voltage across bothends of the other one of said n variable resistors.
 6. The laser drivingapparatus according to claim 1 wherein said n is two and said variableresistors are connected in series, and said voltage detecting means (1)detects a voltage across both ends of one of said variable resistorswhich is connected to a reference potential, (2) detects a potential ofa terminal of the other variable resistor which is not connected to saidone variable resistor relative to said reference potential, and (3)detects a voltage across both ends of said other variable resistor bysubtracting said detected voltage across both the ends from saiddetected potential.
 7. The laser driving apparatus according to claim 1,wherein said n is two, said n variable resistors are connected in seriesand one of the variable resistors is connected to a predeterminedreference potential, and said voltage detecting means detects apotential of a side of said one of the n variable resistors, said sidenot being connected to the reference potential, and said voltagedetecting means detects a potential of a side of the other of said nvariable resistors, said side not being connected to said one of the nvariable resistors.
 8. An optical head apparatus, comprising: the laserdriving apparatus according to any one of claims 1 to 7; means forcondensing rays emitted from said laser driving apparatus onto anoptical information medium; and a photodetector detecting reflected raysfrom said optical information medium.
 9. An optical informationprocessing apparatus, comprising at least: a driving mechanism for anoptical information medium; the optical head apparatus according toclaim 8; a focus servo mechanism using a focus error signal and atracking error signal respectively obtained from said optical headapparatus; a tracking servo mechanism; an electric circuit for realizingsaid servo mechanism; and a power source.